Commit 304b66d2 authored Oct 31, 2024 by Jens Axboe Committed by Wen Zhiwei Nov 14, 2024

io_uring/rw: fix missing NOWAIT check for O_DIRECT start write

stable inclusion
from stable-v6.6.60
commit 003d2996964c03dfd34860500428f4cdf1f5879e
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/IB44K1

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=003d2996964c03dfd34860500428f4cdf1f5879e



--------------------------------

[ Upstream commit 1d60d74e852647255bd8e76f5a22dc42531e4389 ]

When io_uring starts a write, it'll call kiocb_start_write() to bump the
super block rwsem, preventing any freezes from happening while that
write is in-flight. The freeze side will grab that rwsem for writing,
excluding any new writers from happening and waiting for existing writes
to finish. But io_uring unconditionally uses kiocb_start_write(), which
will block if someone is currently attempting to freeze the mount point.
This causes a deadlock where freeze is waiting for previous writes to
complete, but the previous writes cannot complete, as the task that is
supposed to complete them is blocked waiting on starting a new write.
This results in the following stuck trace showing that dependency with
the write blocked starting a new write:

task:fio             state:D stack:0     pid:886   tgid:886   ppid:876
Call trace:
 __switch_to+0x1d8/0x348
 __schedule+0x8e8/0x2248
 schedule+0x110/0x3f0
 percpu_rwsem_wait+0x1e8/0x3f8
 __percpu_down_read+0xe8/0x500
 io_write+0xbb8/0xff8
 io_issue_sqe+0x10c/0x1020
 io_submit_sqes+0x614/0x2110
 __arm64_sys_io_uring_enter+0x524/0x1038
 invoke_syscall+0x74/0x268
 el0_svc_common.constprop.0+0x160/0x238
 do_el0_svc+0x44/0x60
 el0_svc+0x44/0xb0
 el0t_64_sync_handler+0x118/0x128
 el0t_64_sync+0x168/0x170
INFO: task fsfreeze:7364 blocked for more than 15 seconds.
      Not tainted 6.12.0-rc5-00063-g76aaf945701c #7963

with the attempting freezer stuck trying to grab the rwsem:

task:fsfreeze        state:D stack:0     pid:7364  tgid:7364  ppid:995
Call trace:
 __switch_to+0x1d8/0x348
 __schedule+0x8e8/0x2248
 schedule+0x110/0x3f0
 percpu_down_write+0x2b0/0x680
 freeze_super+0x248/0x8a8
 do_vfs_ioctl+0x149c/0x1b18
 __arm64_sys_ioctl+0xd0/0x1a0
 invoke_syscall+0x74/0x268
 el0_svc_common.constprop.0+0x160/0x238
 do_el0_svc+0x44/0x60
 el0_svc+0x44/0xb0
 el0t_64_sync_handler+0x118/0x128
 el0t_64_sync+0x168/0x170

Fix this by having the io_uring side honor IOCB_NOWAIT, and only attempt a
blocking grab of the super block rwsem if it isn't set. For normal issue
where IOCB_NOWAIT would always be set, this returns -EAGAIN which will
have io_uring core issue a blocking attempt of the write. That will in
turn also get completions run, ensuring forward progress.

Since freezing requires CAP_SYS_ADMIN in the first place, this isn't
something that can be triggered by a regular user.

Cc: stable@vger.kernel.org # 5.10+
Reported-by: Peter Mann <peter.mann@sh.cz>
Link: https://lore.kernel.org/io-uring/38c94aec-81c9-4f62-b44e-1d87f5597644@sh.cz


Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Wen Zhiwei <wenzhiwei@kylinos.cn>

parent 2055aa9f

io_uring/rw.c

+21 −2

Original line number	Diff line number	Diff line
		@@ -860,6 +860,25 @@ int io_read(struct io_kiocb *req, unsigned int issue_flags)
		return kiocb_done(req, ret, issue_flags);
		}

		static bool io_kiocb_start_write(struct io_kiocb req, struct kiocb kiocb)
		{
		struct inode *inode;
		bool ret;

		if (!(req->flags & REQ_F_ISREG))
		return true;
		if (!(kiocb->ki_flags & IOCB_NOWAIT)) {
		kiocb_start_write(kiocb);
		return true;
		}

		inode = file_inode(kiocb->ki_filp);
		ret = sb_start_write_trylock(inode->i_sb);
		if (ret)
		__sb_writers_release(inode->i_sb, SB_FREEZE_WRITE);
		return ret;
		}

		int io_write(struct io_kiocb *req, unsigned int issue_flags)
		{
		struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
		@@ -913,8 +932,8 @@ int io_write(struct io_kiocb *req, unsigned int issue_flags)
		return ret;
		}

		if (req->flags & REQ_F_ISREG)
		kiocb_start_write(kiocb);
		if (unlikely(!io_kiocb_start_write(req, kiocb)))
		return -EAGAIN;
		kiocb->ki_flags \|= IOCB_WRITE;

		if (likely(req->file->f_op->write_iter))